Bioprocessing of Microalgae for Extraction of High-Value Products

Microalgae are a rich source of various high-value biomolecules such as lipids, carbohydrates, protein and pigments. However, extraction of multiple high-value products is essential for sustainability and commercial feasibility of the microalgal production platform. Therefore, the first study of this dissertation was focused on optimizing processing parameters for extraction of pigments and functional proteins from C. vulgaris. A wet biomass-to-solvent ratio of 1:5 and 3 extraction stages were required to achieve maximum extraction yield of pigments. Effective protein release from wet biomass was achieved by high-pressure homogenization. Ethanol extraction of pigments affected protein solubility, and an alkaline pH was required to release the same total protein. Concentration of proteins was carried out using a two-stage membrane filtration process. Ethanol treatment and higher pH conditions did not negatively impact membrane filtration, nutritive value, nor the emulsification properties of protein concentrates. The effect of pulsed electric field (PEF) on imparting permeability and enhancing pigment extraction from C. vulgaris was also evaluated. PEF was successful in permeabilizing fresh cells and enhanced the lutein (2X) and chlorophylls yield (4X) at an electric field intensity of 6250 V/cm, pulse duration of 620 μs at a biomass concentration of 56 g/L, followed by a single-stage ethanol extraction for 45 minutes. Up to 14% of the total protein was released after PEF. Extraction of intracellular recombinant proteins from microalgae is usually accompanied by release of impurities such cell debris, nucleic acids, chlorophyll and host cell proteins. One of the major roadblocks in the purification of recombinant proteins is removal of impurities before loading the extract onto the first chromatography column. Hence, the second study of this dissertation was focused on checking the effectiveness of chitosan precipitation on removal of impurities from C. reinhartdii extracts for the purification of a single chain antibody fragment (αCD22scFv) and comparing it to acid precipitation. Chitosan precipitation performed better than acid precipitation in terms of removal of impurities, reducing DNA by 91%, chlorophyll by 98% and host cell proteins by 81%. Capture chromatography (using a Capto Q column) performed on pretreated extracts resulted in 13-20 fold purification of αCD22scFv